Investigators from London, Ontario, divided 60 patients with recently healed distal radius fractures into two groups. Half received whirlpool at 40 degrees C for 15 minutes, during which time they performed wrist and finger active exercises. The other half received hot packs heated to 73 degrees C without performing any exercises. Volumetric measurements were obtained using “a standard volumeter” immediately before treatment, immediately after heating, and again 30 minutes later. The investigators hypothesized that whirlpool would increase hand volume greater than hot pack application due to the “dependent position of the hand during heating.”

The authors found that immediately after heat the hot pack group swelled on average .7% and the whirlpool group swelled 1.9%. Thirty minutes later the difference in volume change was no longer significantly different between the groups.

The authors conclude that whirlpool can be considered when selecting a heat modality for patients with distal radius fracture.

COMMENT: I always have high hopes for blinded, randomized controlled studies. This one let me down. I agree with the authors’ conclusion that whirlpool for this indication is innocuous, but I have a number of issues with their premise and methodology, which may bring their results into question. More importantly, I hope my commentary clears your thinking and helps future investigators design and execute careful, meaningful studies.

The premise that a hand in a whirlpool is dependent is WRONG. Yes, it is dependent when the whirlpool is empty. Under water, however, the pressure of the water pushing IN on the hand equals the pressure of the blood in the veins pushing OUT. The net effect is as if the limb were floating on the surface of the water. After that, the hand can be just below the water’s surface or touching the bottom of the tub, and the edema-producing effect is negated. This misconception about whirlpool dependency is widespread and gets passed along. If you do not believe me, ask a high school physics teacher.

Next, the investigators did not apparently ensure that the level of the hotpacked hands below the heart was equal to the level of the water surface in the whirlpool. It is altogether likely that the table level for the hotpacked hands was higher than the water surface for the whirlpooled hands. If that is the case, a hidden bias for dependency was built into the whirlpool side of the study. Had both groups received hot pack treatment, one group at table top level and one group with their hand resting on their lap, I would expect that the latter group would swell more. Conversely, if there was another group who received hotpacks while their hand was resting on top of their head, they might not have swelled at all.

Then, the hotpack group rested their hands while the whirlpool group performed exercises. Furthermore, agitating water buffeted the whirlpool hands without any similar external mechanical effect for the hotpack group. Two uncontrolled variables. Hmmm.

Finally, they used “a standard volumeter” and noted with references (from 1956 and 1963) that this method of measuring volume has excellent reliability. More cloudy thinking. For instance, they do not indicate how much of the limb in the current study was immersed. If the swelling was mostly in the hand and wrist, that change would be masked if part or all of the forearm was immersed. For instance, a finger could be swollen to twice its normal volume, but if the entire hand and forearm were included in the measurement, the measured change might amount to no more than several percent. Secondly, accurate volume measurements by water displacement depend on the surface area of the water being as small as possible. As an example, tossing a pebble in the ocean displaces as much water as tossing it into a cup of coffee, but the vertical rise in the coffee cup will be noted, whereas not in the ocean. The “standard volumeters” that I have seen have way too much surface area to detect small changes in volume of displaced water.

I hope I have jolted your thinking. I have emailed an abbreviated version of my comments to the authors. I will let you know next month of their response. In the meantime, sign up for Doctors Demystify Current Science, October 26-29, 2017 at Lake Arrowhead. California. Registration deadline is June 15. At the course we will discuss the physics of whirlpool and many other aspects of the science that underpins hand therapy. One therapist commented after the course, “This course will change the way you think about hands forever.” That’s the plan.